Porous Medium
The Porous Medium node adds the Brinkman equations: Equation 4-34 and Equation 4-35 (excluding any mass sources). It has two default subfeatures — the Fluid subfeature where the fluid density ρ(SI unit: kg/m3) and dynamic viscosity μ (SI unit: Pa·s) are defined and the Porous Matrix subfeature where the permeability κ (SI unit: m2) and porosity εp (dimensionless) are specified.
Coordinate System Selection
Select a coordinate system from the Coordinate system list for the interpretation of directions in anisotropic material properties. The default is the Global coordinate system, and the list contains any additional orthonormal coordinate system (except boundary coordinate systems) added under the Definitions node.
The subnodes inherit these coordinate system settings. In particular, the Permeability (in the Porous Matrix subnode) should be set according to the coordinate system selected in this section.
Flow Model
Define if the flow follows a linear or nonlinear pressure-velocity relationship.
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Darcian flow (default) defines a linear relationship characteristic for low Reynolds number laminar flows.
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Non-Darcian flow defines a nonlinear relationship due to inertial or turbulence effects.
Porous medium turbulence model
If in the parent feature node a turbulence model other than Algebraic yPlus or L-VEL is selected, define a model which complements the basic turbulence model and accounts for the influence of the porous matrix on turbulent flow in porous media.
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For Default and Nakayama-Kuwahara specify the Coefficient of subgrid turbulence generation by porous matrix Cstpm which by default is set to 0.212.
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For Pedras-de Lemos, specify the Choice of the Pedras-de Lemos model coefficient. When User defined is chosen, specify the Coefficient of subgrid turbulence generation by porous matrix Cstpm with default value 0.212. Choosing Original results in , while choosing Recalibrated results in Cstpm = 0.18.
Distance Equation
This section is available for the turbulence models Algebraic yPlus or L-VEL. Select how the Reference length scale lref (SI unit: m) is defined — Automatic (default) or Manual:
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For Automatic the wall distance is automatically evaluated to one tenth of the shortest side of the geometry bounding box. This is usually quite accurate but it can sometimes give a too high value if the geometry consists of several slim entities. In such cases, define the reference length scale manually.
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For Manual it defines a different value or expression for the length scale. The default is 1 m.
lref controls the result of the distance equation. Objects that are much smaller than lref are effectively be diminished while the distance to objects much larger than lref are accurately represented.